Snap on/magnetic. Slide ons take to much space, that too the physical locking mechanism will wore off over time. Same thing with snap ons, the physical locking mechanism will wore off over time. But snap ons and magnetic will be a perfect combination. The magnets will act as conductors and also a locking mechanism with out wearing off. That to the snap ons/magnetic can be connected vertically which takes up less space compared to slide ons which need more space to slide on horizontally.

You should make some designs I think 3d drawing would be a handy skill for you. Google SketchUp is amazing software and free to download. You will be able to teach yourself the basics with YouTube fairly quick

Are you studying for some particular career area? Electrical Engineering? Mechanical Engineering?

Try to put in thought to all the reasons why this idea failed before.

Each connection is a cause of unreliability. Think about how to make the connections between the bricks as reliable as a solder in the factory.

Consider how you address the electrical resistance of each connection. What are they made of? Gold is best but expensive.

The current best connectors have resistance still significantly higher than solder.

As this is DC-DC there is no impedance, just resistance. However, each DC-DC converter relies on impedance within itself, so there is something to think about in terms of EM leakage out of the DC-DC converter brick.

Think about how to make them reliable in the long term, wear and tear, and how dirt in particular oils and salts off human touch will affect performance over time.

Think about how much extra material having one case around each module vs one case around a total product as now, the manufacturing cost and the added weight.

These issues has been why this idea has always died in the past, when a highly modular approach was considered, when it went through a rough manufacturing cost.

Consider for example how Anker mades it LC90 torch, it is a kind of modular so you could screw-on different USB socket types instead to make it say USB-C or Lightning. Does that screw-on method carry across better than plug-in?

Google and LG couldn't make modular phones work. What does this mean for Lenovo as the only one left trying?

Look how your drawing looks very similar to this phone modular design.

One way to be creative is to have the fewest bricks and place major components in each, hence say you'd connect only 2 bricks, not need 3+ bricks to make a working system. In a sense this is what Anker is doing right now, because the purchase decision of a charger is correlated to the purchase decision of the device (e.g. "buy new iphone, buy new charger") and the average lifetime of a phone is about the same as the lifetime of a charger, the cables last less so why Anker is separating the cable to be modular from the charger. So there is a lesson - limiting the choices via the USB socket.

One way to makes these reliable is have a limited set of cases which snap around the bricks and bricks must be in a limited set of size+shapes (I think your idea is this already yes?). Then you'd snap together a limited set of fixed size mAh cells (with no casing) with a limited set of DC-DC converters, with a limited set of plug types. Then if someone wanted to say change a 10000mAh Lightning to USB-PD then they'd change the DC-DC converter and the plug but not the cell. I think this is what you are thinking. The extra thought is about doing "just enough modularity" to make a gain.

If you do a BSc on Electrical Engineering, or ideally two degrees with your 2nd in Mechanical Engineering, then they teach these principals - and these the sort of qualifications Anker staff have now.

Ok, I agree with you on the modular phones but this is a modular battery. Connecting modules to the base battery bank will be magnetic with a snap-on lock to lock it in place. The magnets will act as conductors and a secure fit without any movement once it's connected. This will not where off over time. The modular phones connects to modules by have a bread board and pins connecting them. This will result in wear and tare. Screwing in modules mentioned in paragraph 10, will where off. Once a tiny error happen when screwing in the modules, the tread in the plastic will wear off resulting in a faulty module installation. Having a lot of module slots is good. Many people need different things you know. Some people might need high battery capacity and also need lots of USB ports or other people need built in type C cable or lightning cable because they can't carry extra cables. All of these I've tooken into consideration before i made my design. I wanted to have any size modules so like adding another 5,000 mA will be medium sized so most likely it might take up 4 pins. I'm not an expert at electronics because I'm 14 and I'm still learning about electricity and electrical components so can you make it more understandable for my age because i don't understand when you mean "limited set of DC-DC converters"

I Hope You can tell me all the other flaws that this idea has so i can improve on my design.

So as you discharge a lithium cell its output voltage drops, but the USB output of an Anker Powercore does not (you now know why!) it is because there is a DC-DC boost converter making a fairly-constant 5V (ish) output even though the voltage into the DC-DC is slowly dropping from roughly 4.2V to roughly 3.6V.

Inside the DC-DC converter is basically a coil of wire to make the inductor. You can see one here in an example tear-down video

So how in the above video you see the basic "inside" components of your modular design, on the left you have the DC output ports (USB in this case), next to the left is the DC-DC converter (you see the coils) and on the right are the Lithium Ion Cells.

In your design consideration, look at the thicker wires and the solder connections, and on the PCB (the orange rectangle) all the solders between the output (USB ports) and the DC-DC converter.

In a modular design you would have to:- make connectors as reliable as wires- make connectors as efficient as solder- solve the inductance problem between the connectors from the DC-DC converter to the ports.

OK! here is an update, I'm Planning to build a Prototype of my design. So I Must design an actual model of how would the exterior and interior will look like. I would give you an update when I get all the parts and when I make my new design.

Some modules & ideas that would be nice are 1.extra battery2.add on ports lightning/type C/micro/USB type A3. Light bar/battery4.Qi wireless charger transmitter/receiver/battery5. Variable voltage output to power other devices6. Velcro strap to keep modules together in case of drop. Thin and lightweight7. Contacts for extra modules on both sides included click on magnetic covers for when contacts are not in use

The slim 5000mah battery bank might be a good platform to build off and possibly keep the modules a similar size magnetic/snap on . Keep up the good work kid. I'm very impressed with your interest and determination especially at such a young age. I really liked your original Moto mod type idea. A larger model based of the 20,000 would also be useful and desirable.

This is an another update. I have been going through recent problems when i was making my design. For example, not making the pins the right size, not spacing my input pins evenly, and etc. This might take a long time to finish due to the fact that I need to go to school on Aug 30th and I need to do my engineering science fair. I give you another update here or there but it might take some time though.

I do AutoCAD drawing & programming GCODE for CNC machines and you can only learn so much from a book or a class. Most of the stuff I personally learned was through trial and error along with the will to accomplish something. Things will fall into place at the right time. Try not to force it but at the same time, don't give up on trying.